Compact and thin types of image pickup devices are traditionally coming to be mounted in compact and thin types of electronic apparatus such as hand-held telephones and personal computers, and in PDAs (Personal Digital Assistants) and the like, to thereby enable transmission not only of voice information, but also of image information, to and from remote places.
The image pickup devices mounted in these hand-held terminals are very short in the focal length of an image pickup optical system and have aperture F-numbers as small as about 2 to 4. For these reasons, the focal depth at the image side is very small and stringent accuracy is required for positioning in the optical-axis direction of the image pickup optical system with respect to an image pickup plane. In addition, light-receiving sections for photoelectric conversion are arranged at pitches of several micrometers, and so if any dust particles blocking the flux of light incident on the object to be photographed are present on the microlens disposed on a light-receiving element, trouble will occur in object image data.
Solid-state image pickup elements such as a CCD (Charge-Coupled Device) type image sensor or CMOS (Complementary Metal-Oxide Semiconductor) type image sensor are used as the image pickup elements for the image pickup devices described above.
Position-setting methods and dust-proofing methods for the image pickup optical systems of the image pickup devices are proposed in connection with the above. Patent Reference 1, for instance, discloses information on a structure intended to obviate the necessity for focus adjustment during the manufacture of the image pickup device. This structure provided with dust-proofing and moisture-proofing is also adapted to position an image pickup device element and an optical member in the direction of an optical axis by abutting the legs formed integrally with the optical member, on the image pickup device element, and energize this optical member in the direction of the image pickup device.
Image pickup devices capable not only of pan-focus photographing that uses a great depth-of-field with an image pickup optical system fixed, but also of macro-photographing with the image pickup optical system moved, in order to achieve more strengthened functionality, have become available on the market in recent years.
For example, Patent Reference 2 discloses, as an example of an image pickup device capable of macro-photographing, a device that has protrusions and inclined cam grooves formed at alternate positions on an image pickup lens and a tubular holder, moves the image pickup lens in an optical-axis direction by pivoting the image pickup lens, adjusts focus during assembly, and thus enables close-up photographing that uses the inclined grooves.
However, since the above-mentioned solid-state image pickup elements, when used intact, have a spectral sensitivity ranging up to an infrared light region, the infrared light region is cut off before photographic object light reaches the image pickup element.
In connection with the cutoff of the infrared light, some image pickup elements have an infrared light cutoff filter in front of an image pickup lens, as described in Patent Reference 3, for example.
[Patent Reference 1] Japanese Laid-Open Patent Application Publication No. 2003-37758
[Patent Reference 2] Japanese Laid-Open Patent Application Publication No. 2002-82271
[Patent Reference 3] Japanese Laid-Open Patent Application Publication No. 2002-341218
A first problem that the present invention is to solve includes the following.
That is to say, the image pickup devices mounted in the foregoing hand-held terminals are also required to provide higher image quality in response to an increase in the proliferation ratio of these devices, and there are requests for image pickup devices having an image pickup element larger in the number of pixels.
Increasing the number of pixels in image pickup devices intended to obtain higher image quality, however, reduces pixel pitches and correspondingly lessens the maximum permissible size of the dust sticking to the photoelectric conversion plane of the image pickup device. Therefore, current situations are already posing the problem that even if there is any sticking dust that is too small to be visible with naked eyes, image data cannot be obtained since a photographic object light flux is blocked.
In this respect, using the image pickup device described in above Patent Reference 1 is a simple and convenient method not requiring an adjustment process for positioning the image pickup element and the optical member in the direction of the optical axis, and is also a method effective for preventing entry of dust from outside. In this method, however, if microvibration or the like is applied to the device interior for a long time, dust arises from wear due to contact between the legs of the optical member and the isolation wall of a mirror housing/frame or from wear from the abutting sections between the legs and the image pickup element. If the dust sticks to the upper face of the image pickup element, the drawback may occur that since a photographic object light flux is blocked, object image data is affected.
Also, during the zooming or close-up photographing that involves moving an image pickup optical system, mechanical linking to the operating member and driving member for moving the image pickup optical system is required, which permits outside dust to enter from the linking sections and causes a drawback similar to the above.
A second problem that the present invention is to solve includes the following.
That is, image pickup devices for mounting in hand-held terminals are required to be as thick as possible in response to reduction in the thickness of the apparatus in which the image pickup device is to be mounted, and this requirement is difficult to meet by using a conventional ceramic package or resin-molded package. Accordingly, dimensional reduction that includes thinning-down is generally accomplished by, after a semiconductor image sensor chip in which is formed a microlens array functioning as an image pickup element has been mounted intact on the printed circuit board forming the image pickup device, assembling optical system constituent elements and the like and integrating these constituent elements into a single unit.
In addition, these hand-held terminals are carried by users and used under various environmental conditions. In particular, if the image pickup element is exposed to a high-humidity atmosphere for a long time, reliability will decrease since the surface of the image pickup element will corrode or the microlens will be adversely affected.
The image pickup device described in Patent Reference 2, however, has protrusions on the surface of an image pickup lens, and inclined dam grooves in a tubular holder, and pivots the image pickup lens by pivoting the aperture-stop-fitted retainer disposed at the front edge of the image pickup device, and moves the lens in its optical-axis direction along the inclined grooves. Using this construction permits moisture to readily enter from the clearances between protrusion-free sections on the circumference of the image pickup lens and the inside of the tubular holder, thus adversely affecting the image pickup element.
There is also the problem that when the cam grooves or the cam surface is used to move the image pickup optical system along the cam, foreign matter sticking to the cam surface causes trouble with the operation of the image pickup optical system and/or tilts the optical axis of the image pickup optical system.
In addition, these image pickup devices for mounting in hand-held terminals are required to be as thick as possible in response to reduction in the thickness of the apparatus in which the image pickup device is to be mounted.
In terms of this tendency, for the image pickup device described in Patent Reference 2, information on a method of cutting off infrared light is not disclosed and it is unclear how the infrared light is cut off.
For the image pickup device described in Patent Reference 3, because of an infrared light cutoff filter being disposed in front of the image pickup lens, there is the problem that since not only the thickness of the image pickup lens but also that of the infrared light cutoff filter is added as the overall length of the image pickup device, this device increases in overall length, that is, in thickness.
Furthermore, such an image pickup device is very small (1 cm3 or less in volume), requires very delicate handling during manual assembly by an operator, and has been high in assembly cost. Manual assembly also makes it difficult to rapidly respond to a change in demand. For these reasons, it is considered necessary to automate assembly for a reduced cost and for flexible response to the change in demand.
For the image pickup device described in Patent Reference 2, however, there is a need to form protrusions and inclined grooves at alternate positions on the image pickup lens and the tubular holder, match these protrusions and inclined grooves during assembly, and after that, rotate the image pickup lens to prevent it from coming off. Therefore, this device has the problem that it is not of a structure suitable for the automation of assembly.